The principal aims of this project are to understand the perceptual and physiological mechanisms that allow primates, including man, to navigate using visual motion information. Previous work has elucidated the mechanisms of the passive perception of simulated self-motion, but this is a far cry from actually using motion information t guide an ongoing trajectory. There are two primary cues used in visual navigation: the position of targets (and obstacles) and the optic flow information that provides instantaneous feedback about one's immediate trajectory in the world. The experiments in this proposal wil test how motion-sensitive neurons in the higher levels of visual cortex process, combine, and represent these two cues for the guidance of ongoing behavior. The physiological experiments will be directed at two areas at the highest levels of the motion system in dorsal extrastriate cortex: the medial superior temporal area (MST) and the ventral intraparietal area (VIP). We will test how the signals in these areas correlate with performance on a recently developed active steering task. In this task, nonhuman primates control a virtual trajectory presented in a virtual reality setting. This allows precise control of the cues and also enables the physiological experiments that form the core of the proposal. The specific hypotheses under test in the physiological experiments in Aims 1 and 2 concern the mechanisms by which these signals support performance of a complex, natural task. In Aim 3, we will be developing a biologically realistic, experimentally-constrained computational model of how the nervous system controls steering behavior. Successful conclusion of these aims will allow us to understand both where in the brain such guidance is supported, and how the signals there relate to behavioral capabilities. This information is important from a pure scientific perspective, and will also potentially inform the creation of visual prosthetics to assist navigation by visually impaired patients, and could help the development of improved robotic navigation systems.